netdev - Re: [V9fs-developer] [PATCH kernel] 9p/trans

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200729061449.GA19682@nautica>
Date:   Wed, 29 Jul 2020 08:14:49 +0200
From:   Dominique Martinet <asmadeus@...ewreck.org>
To:     Greg Kurz <groug@...d.org>
Cc:     Alexey Kardashevskiy <aik@...abs.ru>,
        v9fs-developer@...ts.sourceforge.net,
        Latchesar Ionkov <lucho@...kov.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Eric Van Hensbergen <ericvh@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [V9fs-developer] [PATCH kernel] 9p/trans_fd: Check file mode at
 opening

Greg Kurz wrote on Tue, Jul 28, 2020:
> > The "fd" transport layer uses 2 file descriptors passed externally
> > and calls kernel_write()/kernel_read() on these. If files were opened
> > without FMODE_WRITE/FMODE_READ, WARN_ON_ONCE() will fire.

There already is a fix in linux-next as a39c46067c84 ("net/9p: validate
fds in p9_fd_open")

> > This adds file mode checking in p9_fd_open; this returns -EBADF to
> > preserve the original behavior.
> 
> So this would cause open() to fail with EBADF, which might look a bit
> weird to userspace since it didn't pass an fd... Is this to have a
> different error than -EIO that is returned when either rfd or wfd
> doesn't point to an open file descriptor ? If yes, why do we care ?

FWIW the solution taken just returns EIO as it would if an invalid fd
was given, but since it did pass an fd EBADF actually makes sense to me?

However to the second question I'm not sure I care :)

> > Found by syzkaller.

I'm starting to understand where David comment came from the other day,
I guess it's still time to change my mind and submit to linus now I've
had time to test it...

-- 
Dominique